The NCI K25 award is specifically designed to support quantitative scientists whose skills have not yet focused primarily on questions of cancer and who wish to become independent investigators and leaders of interdisciplinary cancer research teams. As an econometrician, the award would enable me to receive necessary training and mentoring in cancer research, support my development as an independent investigator, and contribute to the field of cancer economics through the Obesity, Aging, and Cancer Cost (OACC) Study. The OACC Study's primary goal is to investigate the relationship between obesity and the use and cost of breast cancer services. It is hypothesized that obesity among women over age 65 increases the use of breast cancer services and raises the cost of screening, diagnostic, treatment and hospice episodes, because of its effect on breast cancer risk, detection, and progression. Specific aims include: (1) to determine the relationship between obesity and the use and cost of mammography and mammography-related services as measured by screening, diagnostic, and follow-up services;(2) to determine the relationship between obesity and the use and cost of breast cancer treatment as measured by chemotherapy, radiation therapy, breast surgery, and related services;and (3) to determine the relationship between obesity and the use and cost of breast cancer hospice. Using secondary data from the Medicare Current Beneficiary Survey (MCBS), The New Mexico Mammography Project, The New Mexico Tumor Registry, and SEER-Medicare, we will estimate Cox proportional hazard models on the time to episode of care and exponential conditional mean models on the cost of episode to address a timely question in cancer economics: what is the effect of obesity on the economic burden of breast cancer borne by Medicare? The increasing prevalence of obesity, the aging of United States, and the mounting emphasis on cost containment will exacerbate demands on scarce cancer resources nationally and in the Southwest. Greater allocation of resources toward obesity prevention and early diagnosis of breast cancer among obese women may save cancer resources which can then be freed to improve breast cancer screening, diagnostics, treatment, and palliation for all patients.